In my U.S. Pat. Nos. 4,599,877, and 4,796,447, I describe a philosophy of locks that appears to be completely pick-proof. This is achieved by using the key to set a series of lock-controlling elements, then isolating the key and its key slot from the elements, and only then opening the lock if the elements have been set correctly.
In my U.S. Pat. No. 4,599,877 the key sets the elements directly, while in my U.S. Pat. No. 4,796,447, the key sets a series of intermediate elements, called transfer tumblers. These transfer tumblers set the lock-controlling elements and then the key, the key slot, and the transfer tumblers are isolated from the lock-controlling elements. Only after this has happened, can the lock be opened, if the elements have been set correctly.
In the locks described in my prior patents cited, I do not show how a master key can be employed. As is well known in the art, there is often a need to have a master key that can open a number of locks, each otherwise having its own proper key.
Sometimes a Grand-Master key is needed by which a large number of locks can be opened, where each sub-group of locks must be opened by a master key complementary to that sub-group, and where each lock can be opened by its own key. My present invention provides the master-keying described in this paragraph.
I accomplish the above improvements by using a sidebar to co-operate with notches or holes in the lock controlling elements, as will be described in detail below.